On July 12, 2016, the FBI finally closed the files on one of its most famous unsolved cases. They called it the NORJAK case — short for Northwest Hijacking — but you probably know it by the name given to the hijacker, D. B. Cooper. Most people are familiar with the basic facts: that in 1971, a man hijacked an airliner, demanded and received cash and a parachute, and jumped out the plane's back door over the Pacific Northwest and was never caught or identified. Whether he got away clean, or was killed in the attempt, could never be determined. Even though the D. B. Cooper case continues to capture the public's imagination, there is a lot of fact and fiction unknown to many fans.

On the afternoon of November 24, 1971, a man who looked mid-40ish, wearing a business suit, walked up to the counter of Northwest Airlines in Portland, Oregon. Using the name Dan Cooper, he bought a $20 one-way ticket to Seattle, Washington. He was the second-to-last person to board the plane, and while waiting for takeoff, he ordered and drank a bourbon and soda — unfortunately spilling half of it. Once airborne, he handed flight attendant Florence Schaffner a note, which said something to the effect of "I have a bomb which I will use if necessary, this is a hijacking, please sit next to me." She showed it to fellow flight attendant Tina Mucklow and to the pilots. Cooper then asked for the note back, which is why its exact wording is not known.

Schaffner took the empty seat next to him as ordered and he opened a briefcase, and showed her what she described as red sticks with a battery and wires. He then dictated to her the following demands:

Take this down. I want $200,000 by 5:00 PM in cash. Put it in a knapsack. I want two back parachutes and two front parachutes. When we land, I want a fuel truck ready to refuel. No funny stuff, or I'll do the job.

Schaffner conveyed this information to the pilot. Almost nobody on the plane knew anything unusual was happening; the whole episode was handled discreetly. Cooper added that if these instructions were followed, he would safely release everyone on the plane, except for the flight crew.

The airline agreed and contacted the FBI for assistance making the exchange safely. The FBI collected the money from the Seattle First National Bank. Some FBI records say they used a Recordak high-speed microfilm machine to image the serial numbers of all the bills; other records say the bank had the money on hand with its serial numbers already recorded. The airline got on the phone and collected the four parachutes from local contacts. Two hours later, the exchange had been successful, and the plane taxied for takeoff, fully refueled.

Cooper instructed that the plane was to fly a specific route, from Seattle to Portland, to Medford, to Red Bluff, and then to Reno, all while staying below 10,000 feet and keeping the flaps and landing gear down. The plane was a Boeing 727, featuring the nifty "Airstair" rear access stairway under the tail. Cooper had released two of the flight attendants along with the passengers, but had kept Mucklow on board so she could show him how to operate the Airstair.

Frustrated that the money had not been delivered in a knapsack as he'd requested, Cooper began cannibalizing one of the parachute's cords to do what Mucklow thought was tying the bundles of money to himself. About a half hour after takeoff, Cooper ordered Mucklow up to the cockpit with the pilots and closed the door, ordering them not to open it. At 8:13pm, over southern Washington, the pilots got a number of warning lights. The Airstair had been lowered, cabin pressure had dropped, and the cabin temperature fell sharply — it was -7ºF outside. Not knowing whether Cooper had jumped or not, they continued on to Reno as ordered and landed, causing a nice display of sparks (but no damage) as the Airstair briefly scraped the runway. After receiving no response from Cooper over the intercom, they chanced to open the door, and found him gone; all that remained were his clip-on tie, and a ton of cigarette butts. Nobody would ever see him again.

That included the pilots of the two F-106A Delta Darts that had been scrambled from McChord AFB in Washington and followed the 727. But it would have been next to impossible for them to have seen anything; the 727 pilots' best guess was that Cooper had jumped at 8:13pm, three and a half hours after sunset; and the F-106As were about two miles back. Later a C-130 from Hamilton AFB in California also joined the party, following about 5 miles back. They also never saw anyone jump.

As we now know, exhaustive searches of the area never found a thing. The search area was not only densely forested, but huge, especially since nobody knew for sure when he jumped out of the plane. No body was ever found, no parachute. Agents and police combed one likely corridor, but it was clearly hopeless. And unfortunately, misinformation started piling up thick and early. Newspapers began receiving letters almost immediately, claiming to be from the hijacker, but the FBI never felt any of them were authentic. And, somewhere along in there, the initials D. B. replaced the name Dan in some of the FBI agents' notes, by mistake, and that's what made it into the press and what stuck.

It wasn't the only misinformation. You can scarcely find a version of events online or in print that agrees with what I've just given, which was reconstructed from the notes taken by the flight attendants and the FBI. For example, most accounts say that Mucklow, not Schaffner, was shown the bomb; even though the handwritten notes by both of them prove otherwise. It's universally written that Cooper locked the pilots into the cockpit, even though this was not possible on an airliner and the crew had no trouble exiting in Reno. It's just one of those stories that everyone tells, retells, copies and pastes, and gets all mucked up.

The only break the case ever had came in 1980 when 8-year-old Brian Ingram found three decomposing bundles of $20 bills, totaling some $3000 and bound with rubber bands, on a bank of the Columbia River when on a family picnic. Serial numbers matched, and this one find remains the only evidence of Cooper's leap. By examining the sediments on the bills, Portland State University geologists determined that the money had been deposited there naturally with the sediments and not deliberately buried. Few questions were answered by the find, and indeed new ones were raised: Did these bundles fall separately, did Cooper drop them? Was all the money out there somewhere waiting to be found?

What evidence did he leave? 66 fingerprints were recovered, but no matches were ever found. The clip-on tie yielded nothing of value to 1970s investigators, but in 2007, the FBI announced the results of DNA testing from a few small samples found on the tie. They did obtain a partial DNA profile, but this was of extremely limited value: first because they've no proof it came from Cooper himself, and second because they had nobody to compare it to. In 2009, the FBI allowed a group of independent investigators to examine the tie with electron microscopy. Particles of bismuth, aluminum, and titanium were found on it, leading to speculation that he may have worked in a chemical or metallurgy facility, or in manufacturing. It was interesting information that led exactly nowhere.

Out of a pool of 1400 suspects, the FBI seriously pursued a number of them, but all were easily eliminated. Many people have "come forward" over the years claiming to be D. B. Cooper or to know who he was, but none of these claims have ever held up. In short, no likely candidate has ever surfaced. There are any number of books and websites claiming to have finally identified the hijacker, but take them all with a huge grain of salt. Those claims all failed to convince the FBI.

As an example of just how flimsy even the best theories are, consider the suggestion that Cooper was Canadian. Why is this suspected? Dan Cooper was the name of a Canadian character in a Belgian comic book series which had been sold in French-speaking parts of Canada. Also, Cooper had specified that he wanted "negotiable American currency", something an American would have been unlikely to request. It is on the strength of these alone that this fine, useful theory of his Canadian nationality depends.

History has even done us the not-entirely-unexpected favor of furnishing us with conspiracy theories surrounding the hijacking. Some say the whole affair was staged as a coverup to pay Cooper $200,0000 for assassinating JFK. Others believe it was faked by the government in order to distract the public's attention from the United States' humiliating pullout from the Vietnam War. Needless to say, both claims are 100% evidence-free.

I have one favorite factoid that fuels some of the conspiracy mongering around D. B. Cooper: the subsequent life of the airplane. After the hijacking, the plane remained in service with Northwest Airlines (there was no reason for it not to). In 1978, the plane was sold to Piedmont Airlines. Six years later, Piedmont sold it again to a charter company, Key Airlines, where it was given the new tail number N29KA. One of Key Airlines' charter customers was the US Air Force, and until 1991, the plane that D. B. Cooper made famous was involved in skullduggery of its own: making daily flights between Nellis Air Force Base, Las Vegas, and the Tonopah Test Range, all in Nevada. Its passengers were engineers and military personnel involved in the flight testing of the F-117A Nighthawk stealth fighter. Cooper's plane shared these routes with the infamous "Janet" fleet of unmarked 737s that go into Area 51.

D. B. Cooper left us at least two interesting legacies of his own. One is that in 1972, the FAA ordered all 727s to be retrofitted with a device called a Cooper vane, which is a wind pressure activated interlock that prevents the Airstair from being opened while the aircraft is in flight. The other is that recreational skydivers created the tongue-in-cheek Cooper certificate that can be earned by skydiving from a 727. Due to the legal requirement that Airstair-equipped planes have a Cooper vane, the Airstair is typically removed completely when skydivers earn their Cooper certificates.

Did he survive? Only a further discovery of new evidence might ever tell. If he did, then he successfully got away with one of the most famous crimes of the 20th century, and made even the FBI finally throw in the towel.